Actually, a number of Mercedes years and models had issues with this. It is usually due to rust/corrosion at the bottom end of the coil, where it sits in the control arm pocket. The last few inches of the coil sometimes snaps off. It's not very common but I have heard of it several times. It's more of an issue in the salt/rust belts of the northeast... not something you'll usually find on a southern or western car.